The objectives of this research are to utilize model systems in cell culture to provide insight into the following phenomena in differentiating astrocytes, oligodendroglia, and neurons: (1) the interrelations of cholestrerol and dolichol-dolichylphosphate (do1/do1-P) biosyntheses and the role of HMG-CoA reductase in modulating these interrelations, (2) the regulation of do1/do1-P metabolism and dolichol-linked oligosaccharide and glycoprotein (DLOG) biosyntheses, (3) the relation of do1/do1-P metabolism and DLOG biosyntheses to astrocytic, oligodendroglial, and neuronal differentiation , and (4) the role of thyroid hormone in the regulation of do1/do1-P metabolism and DLOG biosyntheses. In all of the experiments proposed, primary cultures of astrocytes, oligodendroglia or neurons, isolated as essentially homogenous preparations, will be utilized. Concerning the interrelations of cholesterol and do1/do-P biosyntheses, we will determine the extent to which these biosyntheses are regulated coordinately at a critical enzymatic step common to both pathways, i.e., HMG-CoA reductase. Concerning the regulation of do1/do-P metabolism and DLOG biosyntheses, we will define the enzymatic steps controlling the regulation of dolichyl phosphate levels and the utilization of dolicyl phosphate for oligosaccharide biosynthesis. Concerning the relation of do1/do1-P metabolism and DLOG biosyntheses to astroglial, oligodendroglial and nueuronal differentiation, two major series of experiments will be important. First, correlation of specific biochemical indicators of differentiation of the three cell types with specific aspects of dol/dol-P metaboslism and DLOG biosyntheses, described immediatlely above, will be accomplished. Second, we will determine whether these biochemical events in the dolichol-linked pathway are obligatory for the specific expressions of cellular differentiation. Thus, we will determine the effect on these expressions of differentiation of inhibition of either (a) dolichyl phophaste biosynthesis, i.e., by mevinolin, or (b) dolichol-linked oligosaccharide biosynthesis, i.e., by tunicamycin. Concerning the role of thyroid hormone importance of this work relates to previous studies which demonstrate the important role of thyroid hormone in brain development, particularly cellular differentiations, and to our preliminary data which indicate a regulatory role for thyroid hormone in the dolichol-linked pathway in at least the astrocytes and oligodendrogia.